Lippage is a condition in floor tiling where one edge of a tile is on a different plane to an adjacent tile. In plain terms this means that one tile is higher than another giving the finished surface an uneven appearance. When large tiles are used on surfaces with compound falls to a floor waste, lippage is inevitable.
The Australian Standard AS 3958.1 (Guide to the installation of Ceramic Tiles) states a maximum 2mm lippage between standard tiles.
A perception of lippage may not necessarily be due to poor workmanship. Sometimes highly reflective surfaces or the angle of natural or manufactured light accentuate otherwise acceptable work.
There may also be an amount of tile warpage which will influence the final outcome.
If you are unhappy with the tiling work that has been performed you should discuss the matter with your builder who has the ultimate responsibility for construction workmanship. If further assistance is required the Ceramic Tilers Association may be able to assist in resolving outstanding matters.